This invention relates to techniques for processing television signals and, more particularly, to an apparatus for temporally processing video signals to improve their appearance.
As described in the above-identified related applications, an electronic video signal (television signal) can be encoded at reduced bandwidth by lowering the frame refresh rate of the high spatial frequency components, while maintaining the frame refresh rate of at least a portion of the low spatial frequency components at the standard rate. If done in a specified manner, this will not cause substantial degradation in the ultimately displayed image, since human vision cannot perceive changes in high spatial resolution information at as fast a rate as it can perceive changes in low spatial resolution information. Accordingly, as has been previously set forth, an electronic video encoding and decoding system can be devised which takes advantage of this, and other, characteristics of human vision by encoding higher spatial resolution video components to be at a temporal information rate which approximately corresponds to the highest rate actually perceived by human vision for such components; thereby eliminating the need to encode these components at a higher rate, which inherently wastes bandwidth. Also, as shown in the prior copending applications, the low spatial resolution information can be generated in a form which is compatible with standard television video, e.g. NTSC video.
It is among the objects of the present invention to provide an improved apparatus for temporally filtering video signals in general and in the described reduced bandwidth type of system. In accordance with the invention, an apparatus is disclosed for temporally processing video signals. A temporal filter is used which enhances temporal response of video at around the peak of the human vision transient system's temporal response (which is around 10 Hertz), and results in moving images which appear sharper.